javascript - Node.JS 中的异步

Question

我对 Node.JS 中的异步和回调有点陌生。您能否告诉我这是否是进行异步调用的正确方法？

function myFunc(schema) {
    async.each(Object.keys(schema), function(variable) {
        for (item in schema[variable]) {
            for (field in schema[variable][item]) {
                // Some operations go here                   
            }
            createDB(item, schema[variable][item]);
        }
    }); 
}


function CreateDB(name, new_items) {
    ddb.createTable(selected_field.name, {hash: ['id', ddb.schemaTypes().number],
        range: ['time', ddb.schemaTypes().string],
        AttributeDefinitions: new_items
    },
    {read: 1, write: 1}, function(err, details) {
        console.log("The DB is now created!");
    });
}

谢谢

Answer 1

这将是一种方法，尽管如此，我不喜欢回调，我更喜欢使用 promises .
这种方法只会将所有错误传播到 cb1，如果您想处理介于两者之间的错误，您应该 wrap them or try to fix stuff .

如果您要在内部 for 循环中执行异步操作，您将获得一些额外的异步重构乐趣。

function myFunc(schema, cb1) {
    async.each(Object.keys(schema), function(variable, cb2) {
        async.each(Object.keys(schema[variable]), function(item, cb3) {
            for (var field in schema[variable][item]) {
                // Some operations go here
            }
            createDB(item, schema[variable][item], cb3);
        }, cb2);
    }, cb1);
}

function CreateDB(name, new_items, cb) {
    ddb.createTable(selected_field.name, {hash: ['id', ddb.schemaTypes().number],
            range: ['time', ddb.schemaTypes().string],
            AttributeDefinitions: new_items
        },
        {read: 1, write: 1}, cb);
}